1. Field of the Invention
The present invention relates generally to downhole operations. More specifically the present invention relates to determining a downhole distance and physical integrity of a line, such as a coiled tube or a wireline, for the purpose of quantizing various effects such as defects, fatigue life, corrosion and payout for various tests, servicing or maintenance. Even more specifically, the present invention relates to methods and computer executable instructions for marking a downhole line and to the detection of same for correlation to the downhole distance and physical integrity.
2. Relevant Technology
During downhole operations in oil well boreholes, for example, it is often necessary to perform maintenance, distribute tools or deliver chemicals to various locations or positions therein having precise, yet differing depths. As such, it is important to know the appropriate depth or distance measurement to accomplish the appropriate objective. Depending upon the particular downhole operation, a downhole line such as a coiled tube or wireline will be inserted into the borehole to assist in the operation.
Conventionally, distance measurements are obtained from counting revolutions of wheels frictionally engaged with the line as the line is inserted into the borehole. With this method, however, only approximate distances are achieved because the wheels are subject to slippage. Although some methods are known for correcting slippage errors, the distance measurements are, at best, still fraught with erroneous data.
Since the wheels used to indicate the distance of the line inserted into the borehole, or payout, are usually above ground near the origination of the line payout, distance measurements are also adversely influenced by permanent or temporary elongation of the line due to load bearings imposed thereon that occur to the line after passing by the wheels. Frequently, this elongation is non-uniform which further introduces error into the payout measurement.
Because the line may be of varying composition, such as between steel or composite coiled tubing, correction factors which account for various loads introducing elongation into the line are often too inflexible to account for the changes as between line composition.
In some wireline technologies, wheel counter systems are replaced with magnetic marking systems for predicting payout measurements. One problem with these systems, however, is caused because the markings are usually emplaced in a non-permanent manner, such as with horseshoe magnets. Then, over time, the magnetic strength of the mark subsides and re-magnetizing operations are necessary. Temperature variations also cause subsiding of the magnetic strength. Again, re-magnetizing is required.
Another problem occurs because these magnetic markings are typically applied to the wireline, during use, as the wireline is fed into the borehole. Since the line is prone to slippage during this insertion period, the markings are potentially exposed to mis-marking thereof.
Still another problem occurs with these systems when measuring payout because the marks are non-descriptive. Thus, it is necessary to track and count these marks in relation to a starting position. This increases labor and system complexity.
Magnetic marking schemes are also used in some coiled tubing technologies, for example, in U.S. Pat. No. 5,469,916, a magnetic identifying mark (referred to as an indicia) is integrated into and resinously cured with the structure of the coiled tube during the manufacturing thereof. Adversely, this too requires the tracking and counting of the mark in relation to a starting position.
Since the marks of this system are introduced during, and integral to, the manufacturing processes, it is a further problem of this system that there is no robustness allowing for modifications or adaptation to the already numerous existing downhole lines.
It is also taught in this patent that magnetic marks wrapped in bands about the coiled tube can cause delamination, or other deteriorating damage, of the coiled tube structure over time if the band is too thick. Disadvantageously, this requires close-monitored quality control systems and fine-tolerance equipment during the manufacturing phase. All of which increase capital costs.
No matter which downhole magnetic marking technology is used, all are problematic when determining payout by counting marks if additional sections of line are spliced together with an older, existing line. This is because the spliced sections must be evenly fitted into the line in increments compatible with the marking schema or the payout counting will be inaccurate. Moreover, when spliced, an extensive history of the line must be transported with the line to other borehole sites to prevent future miscounting of the marks.
During all phases of the downhole operation from insertion through withdrawal, the line is subject to a severe mechanical and thermal environment having significant pressures, immense bending strains and temperature variations. As such, the line is vulnerable to cracking, fraying, thinning, diametral growth, fracture, corrosion and other detrimental problems which can diminish the physical integrity of the line and lead to very short fatigue lives. Although many prior art downhole systems are directed towards determining payout measurements, few are concerned with monitoring the foregoing. Even the ones concerned with monitoring these problems, however, are rudimentarily only interested with diameter and ovality. Yet, unfortunately, even these few when determining diameter and ovality often cannot accurately or reliably identify the section of line experiencing the difficulty.
Accordingly, it is desirous to overcome the foregoing shortcomings and provide improved methods for determining payout and integrity of a downhole line.
It is, therefore, an object of the present invention to provide improved systems and methods for marking a downhole line and detecting same for the purpose of determining payout and physical integrity.
It is another object of the present invention to provide improved systems and methods for marking a downhole line and detecting same that overcome slippage, elongation and track/count problems during payout.
It is still another object of the present invention to provide improved systems and methods for marking a downhole line and detecting same without adversely suffering from the effects of time and temperature.
It is yet another object of the present invention to provide improved systems and methods for marking a downhole line that can be accomplished at a time other than operational use to improve marking accuracy.
It is still yet another object of the present invention to provide improved systems and methods for marking a downhole line that can be adapted to existing downhole lines.
It is a further object of the present invention to provide easily applied systems and methods for marking a downhole line.
It is an even further object of the present invention to provide improved systems and methods for marking a downhole line that facilitates subsequent line splicing.
It is still a further object of the present invention to provide improved systems and methods for marking a downhole line and detecting same that leads to a comprehensive analysis of the physical integrity of the line.
It is a concomitant object of the present invention to provide economically inexpensive systems and methods for marking a downhole line and detecting same.
It is a further concomitant object of the present invention to provide computer executable instructions for achieving or facilitating some or all of the foregoing.
In accordance with the invention as embodied and broadly described herein, the foregoing and other objectives are achieved by providing methods and computer executable instructions for marking an elongate line, such as a coiled tube or a wireline cable, with a plurality of marks and detecting those marks for determining a distance of the elongate line in a downhole or an integrity thereof.
In a preferred embodiment, each mark comprises a plurality of particles having a substantially permanent magnetizing capability adhered to an exterior surface of the elongate line at preselected intervals with an epoxy paint. The particles are arranged at each preselected interval as a plurality of bands. Thereafter, the particles are oriented into a unique magnetic signature for that interval by magnetizing the particles in an appropriate manner to create a magnetic field substantially normal to the exterior surface. Since the mark detection is preferably a Hall effect probe, this facilitates the detection thereof. The magnetic signatures are stored and, once a mark is detected, a correlation is made to a unique position on the elongate line by comparison with the stored magnetic signatures. Preferred particles include samarium-cobalt and neodymium-iron-boride.
Thereafter, the marks can be used to correlate and track defect types and magnitudes, for example, observed as a result of an inspection of the line. Such tracking enables a history of the line to be established which provides for better corrosion control, maintenance and predictions of future occurring events such as expected fatigue life.
The method of applying a magnetic signature to an elongate line is such that this invention is readily adapted to existing elongate lines without requiring expensive manufacturing rework.
These and other objects and features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.